Figure 7: Open and Braced Excavation Problem

(Crisp manual)

Retaining wall

Numerical Analysis of A Novel Form of Underground ConstructionStudent: Bingjie Liu

Introduction

Aim

Methodology

Comparisons from three examples between CRISP and MIDAS

GTS/NX have been carried out as a benchmark process.

Terzaghi Consolidation

Figure 1: Proposed Cable

Stayed Cavern Design, Created

by Professor Anthony Swain

Nowadays due to the rapid growth of urban development, large

underground caverns，which can be used for transport systems and

water supply etc. have been popularly demanded in urban areas. [1] A

innovative construction method for underground caverns ,‘Cable

Stayed Cavern’ (Figure1), has been proposed by Professor Anthony

Swain. However, the ground movements, one of the most obvious

challenges caused by the excavation have to be predicted to prevent

any damages from the surrounding structures.

1. To provide the methods of setting up

consolidation analysis problems in

MIDAS GTS/NX to other users and

validate the use of MIDAS in

consolidation analysis as well.

2. To model the 3D underground cavern

with corresponding excavation

sequences in MIDAS GTS/NX to find the

resulting ground movements.

The methodology of this project contained the benchmarks between

CRISP and MIDAS GTS/MX to validate the use of MIDAS, which is

being new (a few month) to the department of geotechnical problems.

Three same examples were applied in both programs and the results

were compared to verify MIDAS. After benchmarking these two

programs, MIDAS has been used to model the 3D cavern with

corresponding excavation sequences.

Benchmarks

Supervisor: Dr. Pedro Ferreira

Msc Civil Engineering

-0.100

-0.090

-0.080

-0.070

-0.060

-0.050

-0.040

-0.030

-0.020

-0.010

0.000

0 10 20 30 40 50 60 70 80 90 100 110

Vertical disp.(MIDAS)

Vertical disp. (CRISP)

Time (Nodal value) (Day)

Ver

tica

l d

isp

lace

men

t (

Nod

al

valu

e)

(m)

-1

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 10 20 30 40 50 60 70 80 90 100 110

Exce

ss P

ore

Pre

ssu

re (

kN

*m

-2)

Excess pore pressure (MIDAS)

Excess pore pressure (CRISP)

Normalized excess pore pressure(Hand)

Time (Nodal value) (Day)

Open and Braced Excavation

This one-dimensional Terzaghi

consolidation problem has been chosen

and is represent in Figure 2. The

pressure on the top surface was kept

constant during the consolidation

process and the drainage constraint is

only applied at the top, i.e. set to zero

pressure, while other edges were

undrained to allow excess pore pressure

to build up then dissipate to the surface.

Figure 2: Terzaghi

Consolidation Problem

(Midas manual)

Figure 3: Mesh

example for

MIDAS

Figure 4: Mesh

example for

CRISP

Figure 8: Mesh example for MIDAS

Figure 9: Mesh example for CRISP

Figure 5: Vertical Displacement against Time for Corresponding

nodes in CRISP and MIDAS

Vertical Displacement

Excess pore pressure

Figure 6: Excess pore pressure against Time for corresponding nodes

in CRISP and MIDAS

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.090

0.100

0 1 2 3 4

Ve

rtic

al d

isp

lace

me

nt

(No

de

Val

ue

) (m

)

X Coordinate (Node value) (m)

MIDAS (super imposed element method)(4-node- element)MIDAS (change property method)(4-node-element)CRISP

Basement Heave

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.090

0.100

0 1 2 3 4

Ve

rtic

al d

isp

lace

me

nt

(No

de

Val

ue

) (m

)

X Coordinate (Node value) (m)

MIDAS (super imposed element method)(8-node- element)MIDAS (change property method)(8-node-element)CRISP

Basement Heave

7

7.4

7.8

8.2

8.6

9

9.4

9.8

10.2

-0.070 -0.066 -0.062 -0.058 -0.054 -0.050 -0.046 -0.042 -0.038

Y C

oo

rdin

ate

(N

od

al V

alu

e)

(m)

Horizontal displacment (Nodal value) (m)

MIDAS (super imposed elementmethod)(4-node- element)MIDAS (change property method)(4-node- element)CRISP

Wall Deflection

7

7.4

7.8

8.2

8.6

9

9.4

9.8

10.2

-0.070 -0.066 -0.062 -0.058 -0.054 -0.050 -0.046 -0.042 -0.038

Y C

oo

rdin

ate

(N

od

al V

alu

e)

(m)

Horizontal displacment (Nodal value) (m)

MIDAS (super imposed elementmethod)(8-node- element)MIDAS (change propertymethod)(8-node- element)CRISP

Wall Deflection

2D Embankment Consolidation

Vertical Displacement Vertical Displacement

10m

1.4m

20m

Figure 14: 2D Embankment Consolidation (MIDAS manual)

Figure 10: Vertical Displacement against X Coordinate for

Corresponding Nodes in CRISP and MIDAS (4-node-element)

Figure 11: Vertical Displacement against X Coordinate for

Corresponding Nodes in CRISP and MIDAS (8-node-element)

Figure 12: Y Coordinate against Horizontal Displacement for

Corresponding Nodes in CRISP and MIDAS (4-node-element)

Figure 13: Y Coordinate against Horizontal Displacement for

Corresponding Nodes in CRISP and MIDAS (-node-element)

Figure 15: Mesh example for MIDAS Figure 16: Mesh example for CRISP

-0.70

-0.60

-0.50

-0.40

-0.30

-0.20

-0.10

0.00

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250

Ve

rtic

al D

isp

lace

me

nt

(m)

Time (day)

CRISP (Elastic) MIDAS (Elastic)

Vertical Displacement

-0.18

-0.16

-0.14

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250V

erti

cal D

isp

lacm

ent

(m)

Time (day)

MIDAS (Modified Cam Clay)

CRISP(Modified Cam Clay)

MIDAS (Modified Cam Clay,input pc)

Vertical Displacement

3D Cavern in MIDAS

Figure 17: Vertical Displacement against Time for Corresponding

Nodes in CRISP and MIDAS (Elastic) Figure 18: Vertical Displacement against Time for Corresponding

Nodes in CRISP and MIDAS (Plastic)

Figure 19: Assembled Structures with Cables Figure 20: All Geometry Parts

Figure 21：Effective Vertical Stress Distribution at

In-situ Stage

1. Good agreement between CRISP and MIDAS in elastic analysis.

2. The differences of results between CRISP and MIDAS can be

decreased by increasing the number of nodes per element.

3. Bad agreement between CRISP and MIDAS in plastic analysis

perhaps because of input pre-consolidation pressure 𝑝𝑐′ and initial

void ratio𝑒0.

4. The vertical effective stress redistributed during the 3D cavern

excavation, with decreases after excavation and increases after the

following concrete lining installation.

Conclusions

Reference:

1. Attewell, P.B., Yeates, J., and Selby, A.R. (1986). Soil movements

induced by tunnelling and their effects on pipelines and structures,

Blackie, Glasgow, Scotland, p.325.

Figure 23:Vertical Stress after Soil

excavation

Figure 22:Vertical Stress at

In-situ Stage

Figure 24:Vertical Stress after Shaft

Installation